Idun was selected by the Greater Western Sydney Giants at pick No. 61 in the 2018 AFL national draft.[4] He made his senior debut against Sydney in round 20 of the 2019 season, as a late replacement for injured forward Jeremy Cameron.[5][6] He only managed three games across his first two years before being selected in round one, 2021 and going on to play 21 out of a possible 22 games, averaging 5.4 marks and 12.6 disposals per game. He was named the NAB AFL Rising Star nomination for round 23 of the 2021 season.[7]